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Old 03-11-2016, 05:45 PM   #1
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The use of 6 volt batteries

Reaching out to those with knowledge in these things.....

I'm seriously considering the use of AGM batteries to extend the availability of Amp Hours to my 29MV. Presently, my coach has only one 12 volt house battery totaling about 85AH ....

I understand the use of 12 volt AGM connected in Parallel for the purpose of bring up available Amp Hours for use in dry camping issues. This is easy enough.

Example .... two 12 volt AGM batteries rated at 100 Amp Hours each, connected in parallel will give me 200AH.

As I understand it, connecting two 6 volt AGM batteries have to be connected in series to give me a 12 volt battery system. Those same two 6 volt batteries rated at 200 AH each, connected in series, will give me a 12 volt battery system with the availability of 200A Amp Hours.

My question:
Where did the additional 200AH of the second battery go...??
Is that additional 200AH just lost...??
Is it available in a longer time frame usage of the total Amp Hours of the two battery system...???
Why would anyone use a couple of 6 volt batteries (in place of 12 volt batteries) if half the Amp Hours would be lost....???

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Old 03-11-2016, 07:16 PM   #2
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I think it's 200AH @ 6V . . .
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Old 03-11-2016, 07:39 PM   #3
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go to the Interstate Battery info on the web, it shows all the amp hour ratings of 12v. vs 6v. batteries etc., two 6v. batteries are way more efficient with at least double as I recall storage capacity vs. two 12v. batteries...
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Old 03-11-2016, 07:44 PM   #4
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The 6V batteries are true deep cycle batteries. No amp-hours are lost. I have two Trojan T-105 6V batteries at 225AH. Each weighs about 62 lbs. I paid about $240 for the pair.
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Old 03-11-2016, 08:06 PM   #5
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Quote:
Originally Posted by Boudreaux View Post
.

My question:
Where did the additional 200AH of the second battery go...??
Is that additional 200AH just lost...??
Is it available in a longer time frame usage of the total Amp Hours of the two battery system...???
Why would anyone use a couple of 6 volt batteries (in place of 12 volt batteries) if half the Amp Hours would be lost....???

That is a tough one to explain... I will be using Deep Cycle batteries in the explanation below...

When you are connecting 2 (6volt) batteries in SERIES you will be doubling the voltage (VOLTS) of the battery bank (IE.. 6 volts (200Ah) + 6 volts (200Ah)=12Volts @200Ah. You would need two of the above series battery banks wired in parallel to double the capacity to 400Ah.

Now lets say you are connecting those same 2 (6volt) batteries in PARALLEL you will be doubling the capacity (Ah) of the battery bank (IE.. (6 Volts) 200Ah + (6volts)200Ah=400Ah @ 6 volts) while maintaining the voltage of one of the individual batteries in this bank.

So why use (2) 6 volt (200Ah) batteries opposed to (2) 12 Volt (100 Ah=200Ah)batteries? Cost and package size. The 12 volt cousin of the 6 volt batteries cost more (for the same Ah rating), and their package size is larger, which some RV's can not handle. But either way... 200Ah is 200Ah, whether it is in the form of (2) 6 volt batteries or (2) 12 volt batteries. They will have the same performance (length of time that it takes to discharge).

The one thing most people do not take into consideration is that of the 200Ah of the battery bank (series or parallel) you only can use 100Ah. This is the 50% rule. In other words, you should never discharge the battery bank voltage lower than 12.0 volts which is approximately the 100Ah level of the 200Ah capacity battery bank.

I hope this makes it a little easier to understand
Don
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Old 03-11-2016, 08:59 PM   #6
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Don did a great job of explaining voltage and amp hours.
The other issue that may need touching on is the difference between marine deep cycle and true deep cycle batteries. Marine deep cycle are substantially less costly because they are built on the same manufacturing line as regular 12 volt car batteries. True deep cycle 12 volt batteries may look the same from casual observation but that's where similarity stops. The cases are different inside allowing for
a much thicker plate and fewer plates. They are built for repeated deep cycling of charges and discharges. They are substantially heavier then there marine counter part in weight.
Don is right, 12 volt deep cycle batteries are more expensive then there 6 volt counterpart. Mainly because there is a lot more 6 volt batteries used in commercial use and golf carts which helps bring the price down.
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Old 03-11-2016, 10:39 PM   #7
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No matter which way you decide to go ( 6v or 12 v ) it's best that the batteries are matched: same make, model and age.

If not matched, the weaker will become parasitic on the other(s)

For many of us, when we buy a new RV that comes with a dealer installed 12 v battery, we add a second or third one right away. That's what I did.

In several years, when it time to replace, I Will consider converting to 6V arrays.

Meanwhile, Im very happy with my 12 V batteries
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Old 03-11-2016, 11:50 PM   #8
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A better way to compare batteries is to use their energy storage capacity measured in kWh (kilo watt hours). A Trojan T-105 6v battery can store 1.5 kWh of energy while a Trojan 27TMH 12v battery can store 1.54 kWh of energy. The two 6v batteries must be connected in series and will provide 3 kWh while the two 12v batteries must be connected in parallel and will provide 3.08 kWh. As has been mentioned the 12v batteries are larger in size and take up more space. An advantage of the 12v batteries is if one of the batteries fails you can disconnect it an still have 12v to operate your RV but if a 6v battery fails you are out of luck until it is replaced.
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Old 03-12-2016, 08:20 AM   #9
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Originally Posted by ODH View Post
A better way to compare batteries is to use their energy storage capacity measured in kWh (kilo watt hours).
Yes, kWh is the ideal way of measuring their capacity, but in the RV world Ah, Amps and Volts are a way of life. When you are researching batteries for a purchase, the common thread between choices looked at is Volts and Ah. and the 20 hour rating (@ 25 amp load).

When you look at a Trojan T105 (220Ah) vs a T145 (260Ah), you need to make the decision as to do you need those extra 45Ah and is it worth the money to pay for them. The difference between the 2 is pretty much thicker plates, a slightly larger battery case and a few dollars more... But the actual Ah is a difficult to track without a quality monitor. So, the majority of RVers use Voltage to measure their usage. The most common method is Ah relation ship to Voltage remaining in the battery. If you have a 220Ah battery and you are dry-camping overnight and you wake up to find your battery is at the 50% level (about 12.0 Volts) you have used your allowance of 110Ah from that battery. Then you need to replenish the Ah to start the process again. Granted, there are monitors that will give you %Ah used, actual Ah used, but that to most RVers is an option they are not going to purchase.

I actually have the capabilities for watching the Ah in and out of my system, for my SOLAR/TT, but 99% of the time I monitor the voltage.. It is close enough for RVing.

kWh will only confuse the average RVer, but if you wanted to calculate it out you do have the approximate Ah at a specific voltage chart to calculate the Kw hrs.

Just my thoughts,
Don
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Old 03-12-2016, 08:21 AM   #10
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You need to compare the two battey types in a specification guide -
http://www.trojanbattery.com/pdf/TRJ...dSpecGuide.pdf

Compare the Trojan 27TMH 12V Battey to the Trojan T105 6V Battery using same specs columns...

27TMH 12VDC 117AHs Cap 175 Minutes @25AMPS (2.9Hrs) 47LBS
two connected in parallel gives you this...
12VDC OUTPUT 234AHs Cap 350 Minutes @25AMPS (5.8Hrs) 90LBS
Cost for the two batteries is probably around $300


T105 6VDC 225AHs Cap 447Min (7.45Hrs) 62LBS
Two connected in series gives you this
12VDC OUTPUT 225AHs Cap 447min (7.45Hrs) 128LBS
Cost for two of these GC2 batteries from COSTCO is $180

Bottom line is the two 27TMH batteries will give you 5.8HRS of 12VDC for $300.00

The two T105 GC2 Batteries will give you 7.45Hrs of 12VDC for just $180.00

If you add two groups of these two 6VDC batteries in series you will get 14.9HRs of 12VDC for $360.. Thats not a bad deal actually...

You decide which is best for you...

OOPS I took to long finding the specs and duplicated what others just said... Sorry bout that...

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Old 03-12-2016, 11:30 AM   #11
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The basic math behind it is Ohm's law:

Volts x amps = watts

So 12v*200amps = 2400 watts
or 6v*200amps = 1200 watts

So the overall energy for a 6v is 1/2 that of a 12 volt. Two 6v would get you to 2400 watts, same as the example 12v.

BUT - usually pairs of cheaper "golf cart" batteries have higher amps than many 12 volt batteries. And they can be discharged deeper.
So it becomes a game of balancing cost, capacity, available space, and weight.

In my case, two 6v gave me more capacity than what I could fit in the available space with one big, or two small, 12 volts. And they were a bit cheaper.

Some people go with 2 or 4 6v, some are happy with 1 or 2 12v. Depends on your priorities for the 4 selection criteria listed above.
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Old 03-12-2016, 12:35 PM   #12
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Quote:
27TMH 12VDC 117AHs Cap 175 Minutes @25AMPS (2.9Hrs) 47LBS
two connected in parallel gives you this...
The Trojan 27TMH battery is actually rated at 200 min at 25 amps and weighs 61 lbs. However, this rating is not representative of the actual loading on an RV battery. The normal load on an RV battery is much lower than 25 amp and is intermittent in nature. Therefore the kWh rating is a much better guide to use. As for being confusing, how many post do you see that people erroneously assume that when you connect two 6v batteries you double the amp hrs. This does not happen if you use kWh.
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